1. Field of the Invention
The present invention relates to a press exchangers and extrusion of tubes.
2. The Prior Art Expanded
For hydrostatic extrusion a billet is inserted in a pressure chamber formed by a high-pressure cylinder, a die with an opening having the cross-section desired in the product manufactured, and a pressure-generating punch which, when inserted into the cylinder, generates the pressure necessary for the extrusion in a pressure medium surrounding the billet, thus influencing the billet from all sides. For extruding tubes a mandrel is required to shape the hollow in the tube. Equipment now in use for extruding tubes is shown and more fully described in U.S. patent application of Jan Nilsson et al; Ser. No. 145,184, filed May 20, 1971, U.S. Pat. No. 3,751,958. In this extrusion equipment the forces exerted on the mandrel are taken up entirely inside the pressure chamber and transmitted to the die by a spacer tube. The pressure exerted on the inner end surface of the mandrel and which must be taken up by the spacer tube is extremely high and the wall of the spacer tube must therefore be strong. The pressure is F= .pi.d.sup.2 /4P if d= the diameter of the mandrel and P the pressure in the pressure chamber. This pressure is between 10 and 20 kbar. The equipment is operative and permits satisfactory charging of the pressure chamber. However, the spacer tube takes up space in the pressure chamber which, among other things, is uneconomical.
For pure hydrostatic extrusion, that is, extrusion without any axial force apart from the liquid pressure operating directly on the billet, tubular pressure-generating punches have not been successful so far. Internal overpressure causes the punch to snap while external over-pressure causes it to be compressed.